I wonder if making platforms liable for providing the identity of content producers is a fair balance between providing the platform immunity and allowing those potentially harmed by content to pursue the content creator if needed.
Sites could still allow anonymous communication, but it would need to vet it first and assume liability.
You can't go out in public in a mask and say "John Smith eats worms" (when he doesn't) and not have any repercussions.
This is also how is has stood throughout American history. The foundation of the US was built on anonymous/pseudonymous pamphlets and secret communications between the "Founding Fathers."